A network requiring reliability commonly has redundant configuration such as a “1+1 protected path configuration” in order to prevent interruption of service when a failure has occurred. The 1+1 protected path configuration allows a continued operation of service, by setting two communication paths corresponding two respective path setting sides (or path setting directions) of a work side and a protect side, and by switching a working path that is a currently operating path on the work side to a spare path on the protect side when a failure has occurred on the work side.
In the case of conventional networks such as SONET (Synchronous Optical NETwork) or SDH (Synchronous Digital Hierarchy), setting of communication paths is performed under central control of a network management system, and a technology of UPSR (Unidirectional Path Switched Ring) is employed for setting the 1+1 protected path.
Regarding path switching (Path Switch), as attributes thereof, a “revertive mode”, a “path switch default direction”, and a “wait-to-restore timer value” are used.
The revertive mode is a mode for performing the following operation. In principle, a work side is set as a path switch default direction, and a communication path set on a path setting side (or a path setting direction) identified by the path switch default direction, that is, on the work side, is operated as a working path in an initial state. When a fault has occurred on the work side, a working path is switched to the protect side so as to continue the operation. Thereafter, when any failures have not been detected on the protect side during a time period of wait-to-restore timer value after recovery of the fault on the working side, a working path switches back to the side identified by the path switch default direction, that is, to the work side.
A non-revertive mode is a mode for performing the following operation. When a fault has occurred on the work side, a working path is switched to a spare path on the protect side so as to continue the operation, and even when the fault on the work side is restored, the operation is continuously performed by using the currently working path on the protect side. The above is the operation in the non-revertive mode.
The path switch default direction indicates a normally used one of the work side and the protect side in the operation of the revertive mode, and a communication path set thereon is operated as a working path in the initial state. The wait-to-restore timer value is a time period for monitoring that there are no faults occurring on the protect side, in the case of the revertive mode, after recovery of the fault on the work side, in order to switch back a working path from the protect side to the work side.
FIG. 1 is a diagram illustrating an example of relations between attribute values and modes of path switching. In the revertive mode, the path switch default direction and the wait-to-restore timer value are needed. In the non-revertive mode, the path switch default direction is needed, but the wait-to-restore timer value is not needed.
In networks utilizing SONET/SDH and DWDM (Dense Wavelength ivision Multiplexing), attention is now being paid to a path setting method utilizing GMPLS which is expected to simplify the maintenance of a network because communication paths can be autonomously set in the network by GMPLS.
Standardization of GMPLS is now being promoted and a 1+1 protect path mounting method is being investigated therein (for example, RFC4872). Therein, identifiers named a label switch path ID (LSP ID) (defined in RFC 3209) and an association ID (Association ID) (defined in RFC4872) are used to relate a communication path on the work side (a work-side path) to a communication path on the protect side (a protect-side path). The label switch path ID is an identifier for identifying an end-to-end path and the Association ID is an identifier for identifying the other path paired therewith in a redundant configuration.
In addition, in order to distinguish the work side from the protect side, an identifier named a protecting bit (Protecting Bit) (defined in RFC4872) is used. The default value of the protecting bit is “0” which indicates the work side, and the value “1” thereof indicates the protect side. By this method, it has become possible to discriminate between the work side and the protect side of automatically generated communication paths.
FIG. 2 is a diagram illustrating an example of a format of a path setting message including a path message (abbreviated as “Path Msg”) for requesting path setting and a reserve message (abbreviated as “Resv Msg”) for informing of completion of path setting, which is described on the basis of TLV (Type Length Value) utilized in RSVP-TE (Resource Reservation Protocol-Traffic Engineering). In TLV, arbitrary information can be transmitted by describing the type (Type) of a value (Value) and the length (Length) of a structure (Object).
In FIG. 2, a block BL1 of the head two lines is a description about the entire message, and in “Msg Type”, “1” indicates a path message and “2” indicates a reserve message. A block BL2 is a sender template object (Sender Template Object) and a label switch path ID “LSP ID” is included therein. A block BL3 is an association object (Association Object) and an association ID “Association ID” is included therein. A block BL4 is a protection object (Protection Object) and a protecting bit “P” is included therein
Japanese Laid-Open Patent Publication No. 2008-60755 also discloses a signaling technique for distinguishing and managing a work side and a protect side, like RFC4872